1. Field of the Invention
The present invention relates generally to electrical outlet boxes and the like and relates more particularly to certain new and useful improvements in the configuration of such boxes, in provisions for mounting such boxes in a suitable wall opening, and in combinations of the foregoing features.
It will be understood that although the present invention is described with particular reference to electrical outlet boxes which are adapted to house the termination (i.e., electrical connection) between an electrical power cable and an electrical fixture such as an electrical outlet receptacle or an electrical switch, the present invention can be adapted, where desired, for use in other housing for electrical distribution appliances, such as electrical junction boxes, flush type boxes, etc. Accordingly, when used herein, the term "electrical outlet box" is intended to embrace such additional structures.
The usual electrical outlet box is constructed in a generally box-like configuration with a generally continuous sidewall member depending from a back (or bottom) wall, and formed with one or more cable entry ports (hereinafter sometimes referred to as "knockout windows") in the side wall member, which are adapted to permit access to the interior of the box for electrical power cables. One or more electrical power cables are inserted into the box, each through a cable port opening, for connection to (or termination with) the electrical fixture to be mounted in the box. Moreover, in order to prevent debris from entering the box through cable ports that are not utilized, and to minimize fire spread in the event that the electrical appliance housed in the box malfunctions, the typical cable entry ports in electrical outlet boxes are substantially or completely closed by knockout panels which are removably attached to the box wall structure across each port opening.
It will also be understood that although the present invention is described with respect to a rectangularly-shaped electrical outlet box, the invention is equally applicable to other conventionally shaped boxes, including round boxes.
2. Description of the Prior Art
Heretofore, it has been conventional in electrical outlet boxes for the outermost periphery of the box wall structure to be comprised of substantially straight walls or, in the case of a round box, for the wall structure to be located at a substantially constant radial distance from the center of the box. These conventional structures are disadvantageous in certain usages since they cause the electrical power cable and certain box mounting devices to protrude laterally from the outermost periphery of the wall structure, thereby obstructing entry and mounting of the box in a wall opening.
The desirability of the use of a lug or pawl member displaceable by rotation of a threaded screw for clamping an appliance within an opening in a wall structure has been previously recognized.
For example, U.S. Pat. No. 3,090,587 discloses an appliance casing having a flange extending laterally outwardly beyond the periphery of the casing body and a clamping lug threadably mounted within a frame adjacent the perimeter of the casing. Rotation of the threaded screw operates to displace the arm of the clamping lug from a retracted position adjacent the perimeter of the casing body to an extended position which is adapted to engage the adjacent wall structure. Thus, with the lug in the retracted position, the appliance casing may be readily inserted through the wall opening until the casing flange engages the wall surface; thereafter, rotation of the threaded screw displaces the lug arm outwardly until it engages the lug mounting frame, whereupon continued rotation causes the lug to travel linearly along the shaft of the threaded screw until the lug engages the back surface of the wall, thereby clamping the appliance in place.
U.S. Pat. No. 2,401,948 shows a structure similar to U.S. Pat. No. 3,090,587 applied to a device similar to an electrical outlet box, in which the clamping lug is restrained from rotation in only a single direction of rotative movement.
It heretofore has also been recognized in U.S. Pat. No. 3,966,152 that, as applied to the mounting of an electrical receptacle in a suitably sized wall opening, the aforedescribed lug or pawl mounting device are disadvantageous in that the rotational movement of the lug or pawl arm is restrained in only one direction of linear movement. U.S. Pat. No. 3,966,152 discloses the provision of either (i) a pair of parallel planar pawl stops of differing lengths, or (ii) a single planar pawl stop engageable by a hook extending from the pawl member, in order to restrain rotational movement of the pawl arm in both clockwise or counterclockwise directions at a point where the pawl arm is adjacent the back surface of the wall structure in which the receptacle is mounted.
However, although the aforesaid structures of U.S. Pat. No. 3,966,152 restrain rotational movement of the pawl arm in both clockwise and counterclockwise directions, and hence in both forward and reverse directions of linear travel, they each suffer from disadvantages in their manufacture and/or use. Thus, the hooked structure is awkward to fabricate and is subject to breakage; where two planar stop walls are employed, one of the stop walls has a relatively long and narrow unsupported cantilevered portion which is also subject to breakage.